This item is not the definitive copy. Please
use the following citation when referencing this material: Dillon, A., Richardson,
J. and McKnight, C. (1990) The effect of display size and paragraph splitting
on reading lengthy text from screen. Behaviour and Information Technology,
9(3), 215-227.

Abstract

The present paper
reports on an experimental investigation of reader performance and preferences
with a screen-presented journal article. The effects of display size (20 lines
and 60 lines) and sentence splitting on readers' manipulation, comprehension
and subjective impressions are assessed. The results indicate that neither
variable significantly affects comprehension but adjusted manipulation levels
are significantly higher in the small window condition. Splitting sentences
across screens also caused readers to return to the previous page to re-read
text significantly more. Subjective data reveal a preference for larger screens
and high awareness of text format. Implications for future work are discussed.

Introduction

Technological
advances continue to make information presentation via computer screens more
feasible and it is generally assumed that text will increasingly be accessed
on screen as well as, or instead of, on paper (Wright and Lickorish, 1988).
However, until recently concern focused mostly on the legibility of the screen
image (Bauer et al., 1983; Gould et al., 1987) and research has indicated
that particular factors of image quality are crucial determinants of legibility
(see Dillon et al., 1988 for a detailed review). Important as this work
is, it provides no insight into the higher cognitive issues involved in reading
and manipulating computer-based text. Such issues grow in relevance as the
advantages of electronic storage, transmission and presentation of text become
apparent to industry, commerce and academia.

Specifically,
little work has been done on the electronic presentation of lengthy texts
where problems of navigation and location as well as manipulation of the document
arise. With paper, readers have acquired a range of physical and cognitive
skills for manipulating text and the relatively standard format of texts allows
for easy transfer of these skills across the spectrum of paper documents.
How electronic text may best be designed to facilitate similarly easy use
remains an open question.

There has been
some research on manipulation of electronic text, particularly on the relative
merits of scrolling and paging. There is evidence to suggest that readers
establish a visual memory for the location of items within a printed text
based on their spatial location both on the page and within the document (Rothkopf,
1971; Lovelace and Southall, 1983). This memory is supported by the fixed
relationship between an item and its position on a given page. A scrolling
facility is therefore liable to weaken these relationships and offers the
reader only the relative positional cues that an item has with its immediate
neighbours. However, on the basis of a literature review, Mills and Weldon
(1985) report that there is no real difference between scrolling and paging
though Schwartz et al. (1983) found that novices tend to prefer paging (probably
based on its close adherence to the book metaphor).

Scrolling has
also been investigated in conjunction with direction (vertical or horizontal­­—Sekey
and Tietz, 1982), rate (self-paced or machine-paced—Kolers et al., 1981) and
display size (Duchnicky and Kolers, 1983). With reference to direction and
rate, all seem to agree that ideally, lengthy texts should be presented vertically
and at the readers choice of rate. Even so, Kolers et al. (op. cit.) report
that forcing readers to increase their rates by 10-20% does not lead to loss
of comprehension and actually appears to increase efficiency of eye-movements
as measured by rate and length of fixation.

Display size,
however, is less clear-cut. Duchnicky and Kolers (1983) investigated the effect
of display size on reading constantly scrolling text and reported that there
is little to be gained by increasing display size to more than 4 lines either
in terms of reading speed or comprehension. Elkerton and Williges (1984)
investigated 1,7,13, and 19-line displays and reported that there were few
speed or accuracy advantages between the displays of 7 or more lines. Similarly,
Neal and Darnell (1984) report that there is little advantage in full page
over partial page displays for text-editing tasks.

These results
seem to suggest that there is some critical point in display size, probably
around 5 lines, above which improvements are slight. Intuitively this seems
implausible. Few readers of paper texts would accept presentations of this
format. Our experiences with paper suggest that text should be displayed in
larger units than this. Furthermore, loss of context is all too likely to
occur with lengthy texts and the ability to browse and skim backward and forward
is much easier with 30 or so lines of text than with 5 line displays. Of the
experiments cited, only the Duchnicky and Kolers study was concerned with
reading for comprehension and their passages were never longer than 300 words.
Thus the findings on window size bear little relevance to reading of lengthy
texts.

A related issue
to display size and scrolling/paging is the splitting of paragraphs mid- sentence
across successive screens. In this case, which is more likely to occur
in small displays, the reader must manipulate the document in order to complete
the sentence. This is not a major issue for paper texts such as books or journals
because the reader is usually presented with two pages at a time and access
to previous pages is normally easy. On screen however, access rates are not
so fast and the break between screens of text is likely to be more critical.

Research into
reading has clearly demonstrated the complexity of the cognitive processing
that occurs. The reader does not simply scan and recognise every letter in
order to extract the meaning of words and then sentences. Comprehension requires
inference and deduction, and the skilled reader achieves much of his smoothness
by predicting probable word sequences (Chapman and Hoffman, 1977). The basic
units of comprehension in reading that have been proposed are propositions
(Kintsch, 1974), sentences (Just and Carpenter, 1980) and paragraphs (Mandler
and Johnson, 1977). Splitting sentences across screens is likely to
disrupt the process of comprehension by placing an extra burden on the limited
capacity of working memory to hold the sense of the current conceptual unit
while the screen is filled. Furthermore, the fact that between 10-20% of eye
movements in reading are regressions to earlier fixated words and that significant
eye movement pauses occur at sentence ends would suggest that sentence splitting
is also likely to disrupt the reading process and thereby hinder comprehension.

To date, such
issues have received scant attention from researchers. Yet they are likely
to have pronounced effects on the acceptance and usability of electronic text.
The present experiment therefore seeks to determine the importance of such
display characteristics in reading lengthy texts from screen. The study requires
subjects to read a journal article on screen where display size and sentence
splitting are manipulated. The aim is to identify the effect of these
variables on comprehension, reading behaviour and subjective impressions of
the task.

Method

Subjects

Of the thirty-two
subjects who participated in the experiment, 21 were male and 11 were female.
Their ages ranged from 22 to 45, with a mean age of 29. The only criterion
for participation was that the subject had completed at least 2 years, full-time,
undergraduate study and were thus reasonably familiar with academic texts.
Subjects were paid £5 for participation and all reported good or corrected
vision.

Equipment &
Materials

Hardware

Text was displayed
on a high resolution, black on white, A3, Etap 'Atris' screen driven
by a Hewlett-Packard VECTRA microcomputer.

Software

The experimental
interface was specially written and was designed to imitate the basic manipulation
available to readers of printed texts. It facilitated movement through the
document by paging forwards or backwards, jumping to particular page numbers
or to the beginning and end of the text. The commands and their actions are
described in Table 1.

___________________________________________________________

CommandAction

N
Next 'page'

P
Previous 'page'

B
Goto the Beginning

E
Goto the End

No. <enter>
Goto specified page

Q
Quit the program

___________________________________________________________

Table 1. Keystroke
commands and their actions

These commands
were permanently displayed at the foot of the screen. Each screen also permanently
displayed the article title, the current 'page', the total number of 'pages'
and the last seen 'page'. A typical screen is presented in Figure 1.

Insert Figure 1 here

Data logging routines
in the display software captured subjects' input and its time of occurrence
and this was used for later analysis of performance.

Text

The text employed
for this experiment was titled "Geography, war and peace" (O'Loughlin
and van der Wusten, 1986), a 3500 word theoretical analysis of international
conflict. It was chosen so as to be equally unfamiliar to all subjects
in terms of content while conforming to the general style and difficulty of
an academic paper.

Questionnaire

A post-task questionnaire
was designed to elicit information on matters such as ease of use of the interface,
additional facilities that might prove helpful, difficulties subjects had
and the extent to which subjects noticed the format characteristics of the
text.

Task

The task required
the user to read the text for understanding rather than detail. No time constraints
were imposed and they were free to manipulate the text and re-read it in full
or in part as often as they required. When satisfied that they had read the
text sufficiently, the subjects were required to summarise its main points.
Finally, they completed a questionnaire.

Design

A four-condition,
independent subjects design was employed with the size of screen (small and
large) and the text style (split sentence and non-split sentence) as independent
variables manipulated to produce the following set of conditions:

Condition 1: 60
lines - non-split text;

Condition 2: 60
lines - split text;

Condition 3: 20
lines - non-split text;

Condition 4: 20
lines - split text;

In the non-split
sentences conditions (1 & 3) only multiples of complete paragraphs were
displayed on the screen while in the split conditions (2 & 4), there was
no consideration of the paragraph unit with the result that all but one of
the screens split the text mid-sentence.

Subjects were
run independently in a quiet experimental laboratory on the university campus.
They were allowed to adjust the seat and monitor to suit themselves. The experimenter
loaded a practice text and explained the commands to the subject who was then
allowed to practise until satisfied that they understood the workings of the
system sufficiently to proceed.

The experimental
text was loaded and the subject informed that they should read the text for
understanding rather than specific detail and that there were no time pressures
or reading sequence constraints imposed. When the subjects completed this
part of the trial to their satisfaction the system was switched off and they
were requested to write a summary of the article. This, it was explained,
should include the author's main points rather than specific details. Once
more there was no time constraint on this activity and when it was completed
to the subjects' satisfaction they were presented with the questionnaire.

Results

Comprehension
measures

Comprehension
scores were deduced by scoring the subjects' summaries according to a procedure
based on the work of Kintsch and van Dijk (1978). This involves an iterative
propositional analysis of the original text to produce a hierarchy of ideas
or core concepts. The first level analysis reduces the original text to its
basic propositions, these are analysed in turn to produce a second level abstraction
and the procedure continues accordingly until a top level is arrived at where
a global 'gist' of the text is described. Summaries are scored according to
the presence of particular ideas, usually from the second or third level of
the hierarchy (the lowest level being too specific and the higher levels being
too general).

The advantage
of this technique is that it produces a measure of comprehension that does
not rely on simple memory for detail as could be the case if subjects were
presented with questions. It also allows subjects to express everything they
remember about the text and puts little pressure on them to "perform"
or answer correctly though summaries composed of unstructured detail will
not score highly. Therefore it is likely to produce a better measure of comprehension
than a method based on question and answer sets. Acceptance of Kintsch and
van Dijk's theory of discourse is not a prerequisite for using the technique.

The original text
was analysed and a hierarchy of propositions developed. Examination of a random
sample of summaries indicated that for the present text, a second level analysis
was most appropriate and all summaries were scored according to their inclusion
of propositional units from that level (maximum score=60). Figure 2 presents
the mean comprehension scores per condition.

Fig 2. Mean comprehension scores per condition

While there is
a slight trend in favour of larger screens, a 2x2 ANOVA revealed no significant
effect for screen size (F1,28=0.46,
NS) or sentence splitting (F1,28=0.01,
NS), and there was no interaction effect (F1,28=0.13, NS). Therefore it seems that screen size and
sentence splitting have no significant effect on reader comprehension for
this type of electronic text and task.

Reading Times

Time taken to
read the text was computed for each subject. A 2x2 ANOVA revealed no significant
effect for screen size (F1,28=2.97, NS) or sentence splitting (F1,28=0.20, NS) and there was no interaction effect (F1,28=1.12, NS). These results are not too surprising
given the absence of a time constraint and the instruction to concentrate
effort on comprehension of the text.

Reading time
x comprehension

In order to investigate
a possible relationship between time spent reading the text and subsequent
comprehension level a Spearman's Rank Correlation Coefficient was calculated.
This revealed a low overall correlation (rho=0.21, p>.2) and no significant
correlations within conditions. In other words level of comprehension
was not related to length of reading in this instance.

Performance
measures

Obviously, users
of a small screen will need to display more pages than users of a large screen
in order to read similar amounts of text. Thus, gross indices of command usage
offer little insight into any possible manipulation effects. In order to obtain
a better impression of text manipulation only changes in direction of viewing
and jumps in the same direction of 2 pages or more were examined. Each
change of direction or jump of at least 2 pages counted as one manipulation.
In other words if a subject read serially through the text from start to finish,
their manipulation score would be zero regardless of display size. However,
in order to avoid contamination with possible split sentence effects i.e.,
changes in direction resulting from single backward page movements to re-read
text, independent previous page commands were not counted but were analysed
separately. Figure 3 presents the mean adjusted manipulation scores per condition.

Fig.3. Mean manipulation scores per condition

The results were
subjected to a 2x2 ANOVA which revealed a significant effect for screen size
(F1,28=6.33, p<.05), but not for sentence splitting (F1,28=0.90, NS) and
no interaction effect (F1,28=2.56, NS). Given the coding of manipulation that
was employed, the screen size effect does not result merely from the extra
keypresses required to view the same information in the small screen conditions.
It seems that subjects reading from the small screen jump about and alter
their direction of reading the text significantly more than subjects
reading from the large one.

Effect of Split
Sentences

Use of the Previous
Page command was analysed in order to investigate the effect of sentence splitting
on performance. However it was not possible to compare gross usage rates of
the command across conditions as this would have confounded use of the command
to manipulate backwards generally with use aimed at re-reading the start of
the sentence or paragraph that had been split. Thus the use of this command
was coded according to its most likely use. As screen-fill rates were approximately
3 and 9 seconds for the small and large screens respectively it was possible
to identify cases where the command had been issued and the resulting screen
not even fully displayed. Similarly, where multiple repeated use occurred
it was considered that these were more likely to reflect occasions when the
subject was re-tracing the argument or attempting to locate a particular piece
of text rather than re-read the split sentence, and accordingly, these were
overlooked. Therefore, only combinations of Previous Page - Next Page, where
the former command displayed the screen for longer than the screen-fill time,
were interpreted as indices of the effect of sentence splitting on performance.

It was hypothesised
that sentence splitting would increase the occurrence of this command sequence
and examination of the data between individual conditions confirmed this.
The mean usage level for condition 4 (small, split) was 3.88 (s.d.=2.47),
over twice that for condition 3 (small, non-split) which was 1.75 (s.d.=1.75).
A one-tailed t-test indicated a difference at the 5% level (t=1.98,
df=14, p<.05). The mean usage levels for conditions 1 (large, non-split)
and 2 (large, split) were 0.1, (s.d.=0.93) and 1.50 (s.d.=2.33) respectively.
Though the mean levels were in the hypothesised direction this difference
was not significant.

Combining the
conditions according to the split/non-split distinction indicated that usage
levels were twice as common in the "split" conditions. Mean combined
level for conditions 2 and 4 (split sentence conditions) was 2.69 (s.d.=2.63)
and for conditions 1 and 3 (non-split sentence conditions) the mean level
was 1.38 (s.d.=1.41). A one-tailed t-test between these conditions was also
significant (t=1.76, df=30, p < .05).

These results
seem to indicate that splitting sentences across screens is likely to result
in increased use of the previous page command as the reader turns back to
recapture the sense of the text portion being read.

Questionnaire

The questionnaire
contained a variety of items aimed at eliciting subjects' views on issues
such as the range of facilities offered, improvements they would like, problems
they encountered and whether or not they noticed certain experimental manipulations.

None of the available
commands was rated as difficult to use. On a scale of 1 (difficult) to 5 (easy)
all of the commands' median ratings were 5, with only one subject rating one
command (No.<enter>) as difficult. The Next Page and Previous Page commands
were rated as most useful (median ratings 5 and 4 respectively on a scale
of 1 to 5, where 5 implies very useful). The End and the No.<enter>
command were rated as least useful (median ratings of 3 in both cases). There
were no significant rating differences observed between conditions.

Subjects were
asked to rate the on-screen information on a scale of 1 (not helpful)
to 5 (very helpful). The median ratings were 3 for Title, 4 for Page X of
Y and 2 for Last Seen Page Number. There were no significant differences observed
in the ratings between conditions. Thus, only the information about current
position in the text was seen as particularly useful by the current sample.

The text that
the subjects read was formatted such that paragraphs were indented and there
was no right justification. The questionnaire asked subjects to state
whether the text had certain formatting features. The results are summarised
in table 2 below. The correct response is marked (•).

Yes
No

Did the text you
just read have:

_______________________________________________________________

right justification?
11
21 •

blank lines between
paragraphs?
7
25 •

sub-headings in
capitals?
9
23 •

paragraphs indented?*
20 •
11

_______________________________________________________________

*
one subject did not respond to this item of the questionnaire.

Table 2. Responses
to items on text format

In all, 12 subjects
correctly answered all items, nine made 1 error, 5 made two errors and 6 subjects
made three errors. Several of the questionnaires contained comments to the
effect that they were not sure of the answers to some of these items. Thus
in order to obtain some indication of the significance of these distributions
a one-way Chi-square analysis was carried out , though it should be noted
that this procedure assumes a random distribution of responses which might
not be the case with these items. This revealed that the distribution of responses
to the items on blank lines (X2=10.125, df=1, p<.01) and sub-headings (X2=6.125,
df=1, p<.05) were significant. The other two items approached significance
(p<.09 in both cases). Therefore it seems as if subjects were generally
aware of the formatting features of the text they read.

The splitting
of sentences was the only text format manipulated between conditions. Subjects
were asked whether or not the text they had read was split across pages. The
responses were as follows (again, the correct response is marked •):

Did the text you
read have only

complete paragraphs
on a page?

Yes
No

_______________________________________________________________

Condition 1 (large
screen - non-split)
5 •
3

Condition 2 (large
screen - split text)
0
8 •

Condition 3 (small
screen - non-split) 4 •
4

Condition 4 (small
screen - split text)
0
8 •

_______________________________________________________________

Table 3. Subjects'
awareness of the text as complete or split paragraphs

What these results
indicate is that all those who read split text seemed to be aware of it (Chi
square: X2 = 8, df=1, p<.01). Those who read only whole paragraphs showed
a chance distribution of responses (Chi square: X2 = 0.25, df=1, p>.90).

All subjects were
provided with the opportunity to state what improvements could be made to
the interface. While a wide range of suggestions were made there was some
consistency in their responses. Table 4 presents the results.

Suggestion
No. of subjects

Alter page size
8

Scrolling facility
6

Dictionary
5

Highlighting facility
5

Alter text format
4

Contents page
3

Search facility
3

No suggestion
8

__________________________________________________________

Table 4. Subjects'
suggestions for improving sentence presentation.

The relative frequency
of occurrence of the request for a scroll facility suggests that this may
be a more acceptable way of interfacing text manipulation for some users.
Interestingly, 5 of the 6 subjects who requested scrolling were in the small
window/split sentence condition. Similarly, of those who wanted to alter the
page size, 6 were in the small window conditions and wanted larger windows.
The desire for a dictionary may reflect the nature of the text employed which
was a theoretical analysis of a domain unfamiliar to the subjects.

Various other
improvements were suggested by individuals e.g. colour, more information on
the article, a clock, a word count etc. which reflect more idiosyncratic preferences.

Discussion

The results of
this experiment demonstrate that screen size and splitting of sentences across
screens are not simple issues for which clear guidelines may be drawn. While
no significant effect for either variable on comprehension was observed it
would be wrong to conclude from this that any 'reasonable' screen size is
suitable for presenting electronic text or that sentence splitting is not
detrimental to readers' performance.

Trends in the
data indicate that levels of comprehension are noticeably higher in the large
window condition for both split and non-split text. Similarly, reading
from the large screen led to significantly lower adjusted manipulation levels.
Of those subjects who expressed a wish to alter the screen size, three quarters
of them were in the small screen condition and wanted to increase it.
Thus, screen size does affect how readers interact with a text.

The same can be
said for splitting sentences across screens. It caused readers to return to
the previous page twice as often as readers of the non-split text, irrespective
of page size. The fact that all readers of the split text reported noticing
this fact would indicate that, if nothing else, sentence splitting has a nuisance
value that would affect regular users. Therefore the recommendation that should
be made on the basis of this work is that when presenting journal length electronic
text to readers of this type, non-split text on a large screen is a better
format.

Several points
are worth raising with respect to these findings. Firstly, though no significant
effect for display characteristics on reader comprehension were observed in
this study, it must be emphasised that the measure of comprehension employed
is ecologically valid but not very sensitive. As mentioned earlier, it was
selected as the best among a limited range of alternatives. Other researchers
have favoured post-task questions (e.g., Duchnicky and Kolers, 1983) but it
was felt by the present authors that these placed too much reliance on recall
of detail. Multiple choice questions may have been employed but these suffer
from similar limitations and require correction for guesswork on the part
of subjects. Measuring comprehension is a problem for researchers in all areas
where knowledge and learning are dependent variables. In the case of
text comprehension any measure will reflect numerous factors other than text
format, such as verbal reasoning ability and motivation of subjects. However,
it is still felt that the Kintsch and van Dijk method is the most appropriate.
A supplement to this, e.g., asking readers to rate their own level of comprehension
might be a useful addition (though hardly an alternative) to the technique.

Secondly, the
absence of a time constraint on reading the article in this study may have
affected the comprehension scores. If one accepts that text comprehension
is a process by which the reader builds a mental model of the author's message,
then text format is likely to have an influence insofar as it affects the
subjects' eye movements and physical manipulations of the text. Where the
time available to read a text is unlimited, such influences are likely to
have little effect on comprehension. Conversely, where time is limited, by
increasing the cognitive demands on the reader to manipulate and re-scan text
thus reducing processing capacity available for message comprehension, text
format is likely to affect comprehension. This is a testable hypothesis that
only future work can address, but it suggests further caution in drawing conclusions
from the present study.

Thirdly, it must
be reiterated that the "small" screen was a 20 line display which
is close to the typical PC size and therefore cannot be described as
genuinely small. Earlier research has concentrated on screen sizes of
much less and comparatively, a 20 line screen would appear "large"
(though still somewhat smaller than typical paper formats). All
of the subjects in the present study had some experience of reading text from
PCs and it is unlikely therefore that they would have considered the presentation
as small. The "large" display was comparatively very large, approximately
the size of A4 paper, and two subjects exposed to these conditions expressed
a desire to reduce it. As mentioned earlier, the literature on window
size is somewhat contradictory and highly task dependent but it seems likely
that there is an upper limit on what constitutes a good screen size and larger
is not always better.

Fourthly, the
manner in which manipulation was measured in this experiment ensured that
simple measures of paging, which would have been proportionally related to
screen size, were not taken as indices. Rather, jumps and changes in reading
direction were employed. This raises the question of why readers in
the small screen conditions manipulated the text significantly more. The most
plausible explanation is that these readers needed to jump about more in order
to obtain navigational information such as headings, sub-headings, graphs
etc.. However, the text employed had only 3 section headings and no graphics.
Therefore readers in the large screen conditions would have manifest similar
rates of manipulation (as it was coded in this study) if subjects were only
jumping about to headings.

An alternative
explanation is that when reading, all subjects like to check back and re-read
earlier sections or to trace an argument backward and forward. In this case,
readers in the small screen condition would have to jump almost 3 pages to
cover the same amount of text as readers of the large screen had on one page.
The page display record for readers in the large screen condition might therefore
present an inaccurate image of methodical serial reading, whereas in reality
several backward or forward jumps were being made. While this conjecture
matches the observations and evidence from readers of paper articles (Thomas
and Augstein, 1972) it is difficult to draw a firm conclusion one way or the
other without data on within-page reading strategies for the large screen
(i.e., eye movement records).

It is possible
that the nine seconds refill rate for the large screen may have been too great
a deterrent to manipulation of this nature. However the lack of direct comments
(it may have been implied in the request for scrolling) from subjects about
this when asked to suggest improvements would seem to indicate that it is
not as simple as that. Obviously further work is required.

A fifth point
of interest is the level of awareness all readers manifested of the text format.
Without explicit instructions to observe such features, it was expected that
subjects would only answer these items at chance levels of accuracy. However,
the majority of subjects correctly described all features of the text format
and the statistically significant identification rates for split text, blank
lines and sub-heading lettering would suggest that readers notice more detail
about the text than was perhaps expected. This is particularly the case where
the formatting is poor, perhaps suggesting that good design is transparent.

Finally, the role
of task cannot be overlooked. These results refer only to detailed reading
of a lengthy academic article. It should not be assumed that these findings
are transferable to other task domains with other types of text. Even with
similar texts, it is clear that readers employ several strategies for extracting
information depending on their goals (Dillon et al. 1989) and the optimum
display size for such tasks may be very different from that required for detailed
reading.

Conclusion

Optimum display
size remains an issue that requires further empirical attention. The 60 line
screen employed in this experiment received some criticism and may prove to
be too large for tasks of this nature, though its approximation to A4 size
would suggest an empirical comparison with paper is required. Readers seem
to think that a 20 line screen is too small for reading lengthy texts and
although no significant decrement in comprehension levels was observed, the
need to consider the role of time constraints has been raised. Small
screens also lead to greater manipulation though no single cause of this has
been identified.

Splitting text
across screens does not seem to affect comprehension levels but readers take
significant notice of its presence for us to hypothesise that, at least,
it would be a nuisance to regular users. The fact that it causes readers to
turn back twice as often to the previous page regardless of screen size lends
credence to this view.

Further work could
look at other display sizes and other text types. The reading strategy for
this type of material may differ for other texts and thus the display characteristics
may produce different effects. Furthermore, reading strategies may change
over time particularly with increased exposure to screen presented text and
longitudinal studies of reader interaction with this medium are vital in order
to gain an impression of the likely long-term effects of the display on performance.
From a methodological point of view, the analysis and measurement of comprehension
is likely to remain an issue but this must not prevent researchers from examining
it as best they can.

Acknowledgements

This work was
funded by the British Library Research and Development Department and was
carried out under Project QUARTET.

The software was
written by David Wake, Centre for Computing and Computer Science, University
of Birmingham. Experimental assistance was provided by Ms. Sue Coles,
Dept. of Human Sciences, Loughborough University of Technology.

We gratefully
acknowledge Edward Arnold Publishers for permission to use the paper by O'Loughlin
and van der Wusten.